The present invention relates generally to a control for a vehicular mounted apparatus for field application of particulate solids for soil treatment including fertilizers, herbicides, fungicides, insecticides, seeds and the like, and particularly to such an apparatus which is arranged to provide for a substantially uniform rate of application, with the materials being uniformly distributed across the entire spreading width. The improved control system is designed and constructed so as to be inherently reliable and durable, and capable of withstanding the corrosive, if not hostile, environments frequently found in dealing with the spreading of agricultural chemicals and fertilizers. The system is easily, readily, and precisely adjustable to provide a wide range of application rates (output per unit area), with these application rates being coordinated with vehicle ground speed so as to constantly maintain the pre-set application rate even in those instances when vehicle speed changes.
The control system of the present invention provides for an accurate indication of application rates, and includes both a coarse (analog) and a fine (digital) indication of the application rate. The analog indicator represents the percentage of drive pump capacity being utilized while the digital indicator is a measurement of the ratio of volumetric metering/discharge screw rotational speed to vehicle ground speed and provides the operator with an accurate indication of application rate. In addition to its accuracy, the apparatus of the present invention is relatively easy to trouble-shoot and repair in the event of the occurrence of a malfunction, and furthermore, the system is relatively easy to accurately calibrate, that is, to measure the actual output of particulate solids per unit area and re-adjust the output if necessary.
In the past, apparatus for use in the field application of particulate solids including, for example, fertilizers, seeds, and/or herbicides were designed in an attempt to provide for an appropriately, accurately and uniformly metered distribution of such materials. In these prior apparatus, attempts have been made to provide application patterns which remain consistent across the full width of spread, and over the full length of the field, regardless of the actual rate of speed or changes in rate of speed of the vehicle spreader. A commonly known device is one which interposes an externally and manually adjusted metering orifice in the output throat of conveyor moving material out of the supply hopper, and wherein this conveyor is mechanically linked to the vehicle drive. Such devices endeavor to obtain a metered and specified application density across the entire field. These past attempts have not been entirely satisfactory inasmuch as changes of rate of vehicle speed frequently involve a lag in response time required to change the application rate for materials being discharged from the application equipment, with this time lag being manifested in an oversupply or an undersupply of material downstream from the point where the speed or rate change occurred. Generally speaking, in prior known systems, alterations or changes in rate of delivery of particulate solids to the spreading or distribution system have normally been undertaken at points removed from the point of discharge, such as from the point where the vehicle supply hopper delivers material into an initial portion of a conveyor used to transport particulate solids onto a spinner spreader or into an initial portion of an elevating conveyor, then into a distributor device, and finally into pneumatic conveying tubes before discharge at various distances along a boom.
The response time lag for typical or commonly used application equipment is normally approximately two to six seconds. This time delay is normally equivalent to the period of time that the material being spread is resident in and passing through the active portions of the spreader delivery mechanism. In the past, attempts have been made to provide an electronic control and synchronization for spreader devices so as to provide remote in-cab adjustment of application rate, however the environment in which the devices are necessarily used, including a harsh mechanical environment and a hostile chemical environment renders such electronic synchronization devices generally unreliable, and not normally suited for use as a sole control device. In order to render electronic devices sufficiently reliable for use as a sole control, extensive precautions are normally required which add significantly to the cost and accordingly render such devices undesirable. Also, controls, when requiring actuation through a number of components, may contribute to a certain amount of delay. The present system, by contrast, responds immediately to changes in vehicle speed, and hence provides for uniform application rate. Also, in certain installations, for convenience and ease of articulation, a servo system may be employed to adjust the output of a positive displacement pump utilized in the drive mechanism.
A further problem has been due to mechanical damage being caused by the spreading equipment to particles of coated fertilizers, urea, and other fragile materials being spread. The present arrangement, in addition to providing accurate and uniform application rates, further provides a mechanism having operational features which minimize damage to the individual particles during movement or transfer for application to the field.
In order to overcome these control problems, the present invention provides an improved hydraulic-mechanical control system which is capable of providing uniform application of a certain specified amount of material, such as a herbicide, fertilizer, fungicide, or other agri-chemicals onto a field. The uniform application of such materials distributed evely across the entire spread width as well as along the direction of travel is not only economically desirable, but is exceptionally desirable from the standpoint of achieving enhanced production. The apparatus of the present invention achieves these goals and objectives through the use of a hydraulic-mechanical control system having both coarse (analog) and fine (digital) application rate meters, along with means for providing fine adjustment of the output and/or application rate. The arrangement of the present invention utilizes an axial piston pump with a variable and controllable output to drive the metering screw in the final output stage of the spreader, along with means for adjustment of the output. A mechanical vernier control located in the cab operates a remote control cable to adjust the output of the pump and maintain the drive speed of the metering screw at a constant ratio relative to vehicle drive speed. In the present system, drive shafts drive an axial piston pumps with variably controllable swash plates or wobble plates have been found desirable to provide a source of working fluid for the hydraulic motors used in driving the components of the metering system of the present invention.